Medical electrical lead having coiled and stranded conductors

ABSTRACT

An implantable lead which has an increased resistance to fracture and has the capability of continued function after fracture of a conductor. The lead is provided with a coiled conductor which may be monofilar or multifilar and which extends along the length of the lead, running from an electrical connector at the proximal end of the lead to an electrode at or near the distal end of the lead. In addition, the lead is provided with a stranded conductor which is electrically coupled to the coiled conductor at point along the lead body located proximal to the point of expected breakage of the coiled conductor and at a point along the lead body located distal to the point of expected breakage. The proximal and distal ends of the stranded conductor in some embodiments are also mechanically coupled to the coiled conductor.

This application is a continuation of application Ser. No. 08/843,763filed Apr. 21, 2997 now abandoned subject to a CPA application filedJul. 30, 1998.

BACKGROUND OF THE INVENTION

The present invention relates to implantable electrical leads generally,and more specifically to cardiac pacing leads.

The conductors in cardiac pacing leads occasionally have a tendency tofracture due to repetitive application of stress to the conductor. Oneway in which this problem has previously been addressed is byreinforcing the lead body in the area in which stress is to be expected,as in U.S. Pat. No. 5,545,203, issued to Doan et al. This patent isdirected primarily toward reinforcing the lead against fracture due toapplication of compressive forces. Reinforcement of the lead body isalso disclosed in U.S. Pat. No. 5,591,142, issued to Van Erp et al. Ithas also been proposed to reinforce the lead body by means of adding atensile reinforcement as in U.S. Pat. No. 5,231,996 issued to Bardy etal. In this patent, the lead is provided with a non-conductive tensilemember such as a polyester cord, which runs the length of the lead body.Other leads having cords or reinforcements running throughout theirlength are disclosed in U.S. Pat. No. 3,844,292 and U.S. Pat. No.3,572,344 issued to Bolduc. A third proposal for dealing with thepossibility of conductor fracture is to render the portion of the leadbody in direct contact with the conductor conductive by addition ofcarbon or other conductive material, as disclosed in U.S. Pat. No.4,033,355, issued to Ammundson.

SUMMARY OF THE INVENTION

The present invention is directed toward providing a lead which has anincreased resistance to fracture and has the capability of continuedfunction after fracture of a conductor. The lead is provided with acoiled conductor which may be monofilar or multifilar and which extendsalong the length of the lead, running from an electrical connector atthe proximal end of the lead to an electrode at or near the distal endof the lead. In addition, the lead is provided with a stranded conductorwhich extends along the coiled conductor from a point along the leadbody located proximal to the point of expected breakage of the coiledconductor to a point along the lead body located distal to the point ofexpected breakage. The proximal and distal ends of the strandedconductor in some embodiments are electrically and mechanically coupledto the coiled conductor, limiting the extensibility of the coiledconductor, rendering the coiled conductor less susceptible to axiallyapplied tensile forces and also providing for continued electricalconnection to the electrode, in the event that the coiled conductorfractures intermediate the proximal and distal ends of the strandedconductor. In alternative embodiments, the stranded conductor may becoupled only at its proximal or distal end to the coiled conductor ormay simply be located in the same lumen of the lead as the coiledconductor, without mechanical connection to the coiled conductor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an implantable lead in which the presentinvention is practiced.

FIG. 2 is cross-sectional view through the lead of FIG. 1, illustratinga first embodiment of the invention.

FIG. 3 is cross-sectional view through the lead of FIG. 1, illustratinga second embodiment of the invention.

FIG. 4 is a side, cut-away view through the lead of FIG. 1, illustratingthe first embodiment of the invention.

FIG. 5 is a side, cut-away view through the lead of FIG. 1, illustratingthe second embodiment of the invention.

FIG. 6 is a side, cut-away view through the distal portion of the leadof FIG. 1, illustrating the first embodiment of the invention.

FIG. 7 is a side, cut-away view through the distal portion of the leadof FIG. 1, illustrating the second embodiment of the invention.

FIG. 8 is a side, cut-away view through the connector assembly of thelead of FIG. 1, illustrating the first embodiment of the invention.

FIG. 9 is a side, cut-away view through the connector assembly of thelead of FIG. 1, illustrating the second embodiment of the invention.

FIG. 10 is a side, cut-away view through the lead of FIG. 1,illustrating a third embodiment of the invention.

FIG. 11 is cross-sectional view through the lead of FIG. 1, illustratinga fourth embodiment of the invention.

FIG. 12 is a side, cut-away view through the lead of FIG. 1,illustrating the fourth embodiment of the invention.

FIG. 13 is cross-sectional view through the lead of FIG. 1, illustratinga fifth embodiment of the invention.

FIG. 14 is a side, cut-away view through the lead of FIG. 1,illustrating the fifth embodiment of the invention.

FIG. 15 is a side, cut-away view through the a lead according to thepresent invention, illustrating an alternative mechanism forinterconnecting a coiled conductor with a stranded conductor.

FIG. 16 is a plan view of a lead having a rotatable fixation helix,embodying the present invention.

FIG. 17 is a cross-sectional view through the lead of FIG. 16.

FIG. 18 is a side, cut-away view through the distal portion of the leadof FIG. 16.

FIG. 19 is a side, cut-away view through the proximal portion of thelead of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a plan view of a defibrillation lead of a lead in which thepresent invention is practiced. The present invention, of course, mayalso be usefully practiced in the context of other types of medicalelectrical leads, such as cardiac pacing leads, nerve and musclestimulation leads, and so forth.

The lead of FIG. 1 is provided with an elongated insulative lead body10, preferably fabricated of silicone rubber, polyurethane or otherbiocompatible elastomer. At the proximal end of the lead, it carries anelongated defibrillation electrode 12, a ring electrode 14 and a tipelectrode 16, each coupled to a conductor located within the lead body10. Tines 18 are provided in maintaining electrode 16 in contact withthe tissue of the right ventricle. Electrodes 16, 14 and 12 maycorrespond generally to conventionally available pacing anddefibrillation electrodes.

The proximal end of the lead carries a connector assembly, beginningwith a molded lead bifurcation 20, which splits off two of theconductors within lead body 10 to a bipolar, in-line connector assembly24, generally corresponding to the IS-1 connector standard for pacingleads. However, other types of connector assemblies may also be adaptedto practice the present invention. Connector assembly 24 is providedwith a first set of sealing rings 28, a connector ring 32, a secondsealing rings 34 and connector pin 36. Connector pin 36 is coupled tothe conductor which extends through the lead body 10 to tip electrode16. Connector ring is coupled to the conductor which extends through thelead body 10 to ring electrode 14. The conductor coupled todefibrillation electrode 12 extends into connector assembly 22, whichcarries a set of sealing rings 26 and a connector pin 36, coupled to theconductor extending through lead body 10 to defibrillation electrode 12.

In the specific context of the lead illustrated in FIG. 1, the conductorcoupling connector pin 36 to electrode 16 takes the form of a monofilaror multifilar coiled conductor to allow passage of a stylettherethrough, while the conductors coupling ring electrode 14 toconnector ring 32 and coupling defibrillation electrode 12 to connectorpin 30 take the form of bundled, stranded wires, provided with a coatingof PTFE. However, the conductors coupling ring electrode 14 anddefibrillation electrode 12 may take the form of any of the variousconductor types known for use in conjunction with implantable electricalleads. If fewer electrodes are provided on the lead, correspondinglyfewer conductors will be included. One or more physiologic sensors maybe added to the lead or substituted for one or more of the illustratedelectrodes. Also located within lead body 10 is a stranded wireconductor which extends along a length of the coiled conductor and whichserves a mechanism for bridging a fracture of the coiled conductor whichoccurs between the ends of the stranded conductor. In some embodiments,the stranded conductor also couples electrode 16 to connector pin 36,providing both an axial reinforcement and a redundant electricalconnection, as described in more detail below. In other embodiments, theelectrical interconnection between the coiled and stranded conductorsmay simply be the contact between the two conductors which occurs as aresult of both conductors being located in the same lumen of the lead.

FIG. 2 illustrates a cross-section through lead body 10, illustratingthe interrelation of the conductor lumens 100, 102 and 104 withcompression lumens 106, 108 and 110, which are described in more detailin U.S. Pat. No. 5,584,873, issued to Shoberg et al. and incorporatedherein by reference in its entirety. In this view it can be seen thatlumens 100 and 102 contain conductors 112 and 114 which in theillustrated embodiment may take the form of PTFE coated bundled strandedwires having a generally straight configuration. In particular,conductors 112 and 114 may take the form of a PTFE coated, bundled,stranded 49 filar cable formed of seven strands, each strand formed ofseven filars, as described in more detail in U.S. Pat. No. 5,584,873 byShoberg et al. incorporated herein by reference in its entirety. Lumen104 contains a conventional multifilar coiled conductor 116 and a smalldiameter bundled stranded wire conductor 118. Conductor 118 may take theform of a seven filar bundle or cable of MP35N or silver cored MP35Nwire, as described in U.S. Pat. No. 5,246,014, issued to Williams et aland also incorporated herein by reference in its entirety, such thatconductor 118 corresponds generally to one of the seven strands thatmake up conductors 112 and 114. In preferred embodiments, conductor 118may have an outer diameter of about 0.003 inches.

In spite of its small diameter and generally straight configuration,stranded conductor 118 is extremely resistant to fracturing in responseto repeated flexure of the lead body and displays a high tensilestrength. Thus, should coil conductor 116 fracture, redundant, strandedconductor 118 will remain to provide for connection to the electrode towhich coiled conductor 116 is coupled. If the stranded and coiledconductors are uninsulated from one another, they make contact with oneanother at multiple points along the lead body, so that a break of thecoiled conductor occurring between the ends occurring between the endsof the stranded conductor will be bridged. The ends of conductor 118 mayalso be mechanically coupled to the coiled conductor 116 and therebyserve to maintain the structural integrity of the lead, preventingpartial disassembly due to applied tensile forces. If the lead isremoved, conductor 118 may thus also serve as a reinforcement, allowingtraction force to be applied to the distal end of the lead duringextraction. In either case, conductor 118 allows for continuedfunctioning of the lead after fracture of the coiled conductor 116,allowing for replacement of the lead, when convenient, withoutinterruption of the therapeutic function of the pacemaker or stimulatorto which the lead is coupled.

In some embodiments of the invention, conductor 118 is uninsulated alongits length and thus makes contact with conductor 116 at various pointsalong the length of the lead. In such embodiments, it is to be expectedthat the conductor 118 will serve as both a redundant conductor,coupling the connector pin 36 to the electrode 16, and as a conductivebridge between the broken ends of the conductor 116, as it will be incontact with the conductor 116 on either side of the break. With thisstructure, changes in overall impedance between the connector pin andelectrode are expected to be relatively small, allowing for essentiallyundiminished performance of the lead. Alternatively, conductor 118 maybe provided with an insulative coating of PTFE or other insulativematerial. In such embodiments, conductor 118 will serve as a redundantconnector, connecting connector pin 32 to electrode 16, and uponfracture of conductor 116, a substantial change in connector pin toelectrode impedance will be manifested. In the context of implantablestimulators capable of monitoring changes in lead impedance, thisprovides the physician and/or the device itself with a mechanism fordetecting the fracture in 116. However, within the context of thepresent invention, the fracture can be detected without the seriousconsequences which would otherwise be associated with disconnection ofthe electrode 16 from the connector pin 36. In the context ofimplantable stimulators having the ability to automatically adjuststimulus pulse amplitude and input amplifier sensitivity, the device mayrespond to the change in lead impedance by noting the occurrence of afracture in conductor 116 and may correspondingly alter its programmedparameters in order to restore performance essentially to that precedingthe fracture of conductor 116.

FIG. 3 is a cross-sectional view through an alternative embodiment ofthe lead illustrated in FIG. 1, in which all labeled elements correspondto identically labeled elements in FIG. 2. The embodiment illustrated inFIG. 3 differs from that illustrated in FIG. 2 only in that strandedconductor 118 is located within the lumen of conductor 116, rather thanexternal to conductor 116. This embodiment may be particularlyadvantageous in the context of leads, such as epicardial electrode leadsor some nerve and muscle stimulation leads which do not require passageof a stylet through the lumen of coil conductor 116.

FIG. 4 is a side, cutaway view through the lead of FIG. 1, illustratingthe first embodiment of the present invention, also illustrated in FIG.2. In this view, it can be seen that stranded conductor 118 is looselyspiraled around coiled conductor 116 along the length of the lead,facilitating flexure of the lead body and the conductors locatedtherein. If the ends of conductor 118 are mechanically coupled toconductor 116, this structure also allows for a limited amount of axialelongation of the lead body and conductor 116 along the length ofconductor 118. All other labeled elements correspond to thoseillustrated in FIG. 2.

FIG. 5 shows a side cutaway view through the second embodiment of thelead of FIG. 1, also illustrated in FIG. 3. In this view, the strandedconductor is shown arranged loosely within the lumen of coiled conductor116. All other labeled elements correspond to those illustrated in FIG.2.

In the embodiments illustrated in FIGS. 2, 3, 4 and 5, conductor 118 maybe insulated or uninsulated, as discussed above, depending on whethercontact between the two conductors along their length is desired. Analternative embodiment in which the stranded conductor is desired to beinsulated from the coiled conductor along some portion of its length mayemploy a separate lumen in the lead body for the stranded conductor,intermediate its points of connection to the coiled conductor. Anadditional alternative as discussed below may employ a tubular,insulative sheath within or around coiled conductor 116 to insulate itfrom conductor 118.

FIGS. 6 et seq. show basic mechanisms which may optionally be employedto mechanically interconnect the stranded conductor 118, the coiledconductor 116, electrode 16 and connector pin 36. These illustratedinterconnection mechanisms are intended to be exemplary, and may ofcourse, be employed in conjunction with other components of implantableleads, including other types of electrical connectors such as connectorrings, corresponding to connector ring 32 and to interconnect theseconductors with other types of electrodes and to interconnect thesecomponents with other lead components such as physiologic sensors suchas pressure sensors, oxygen sensors, temperature sensors and the like.

FIG. 6 is a sectional view through the distal portion of the leadillustrated in FIG. 1. In this view, the interconnection of conductor116, conductor 118 and electrode 16 is visible. Extending distally fromthe defibrillation electrode 12, the lead takes the form of a moldedpiece part 228, which carries ring electrode 14, which is in turncoupled to stranded conductor 112 (not visible in this view). Electrode16 as illustrated is a steroid-eluting electrode, provided with amonolithic controlled release device 222 located within a chamber withinthe electrode. Electrode 16 is coupled to a coiled conductor 116 and 118by means of an external crimping sleeve 224, which compresses conductor118 against conductor 116 and compresses conductor 116 against theproximal portion 220 of electrode 16. Other types of tip electrodes,including screw-in electrodes may of course be substituted for electrode16. Similarly, other mechanisms may be employed to interconnectconductors 118 and 116 and electrode 16, including welding, swaging,crimping and combinations thereof, including mechanisms as disclosed incommonly assigned, copending U.S. patent application Ser. No. 08/657,577by Boser et al, filed Jun. 7, 1996, now U.S. Pat. No. 5,676,694 and U.S.patent application Ser. No. 08/439,332 by Swoyer et al., filed May 11,1995, both incorporated herein by reference in their entireties.

Conductor 114 passes through an internal lumen 100 within lead body 10,and has its insulation removed in areas in which it passes through thecross-bore crimp sleeve 212. The distal turn of electrode coil 12 can beseen at 12A as it passes through the perpendicular cross-bore throughsleeve 212. The sleeve 212 is crimped to the conductor 114 and a portionof the distal turn of electrode coil 12 is inserted through the crossbore and the entry and exit points of the coil are laser welded to thesleeve. External polymeric sleeve 230 is slid over the distal ends ofconductor coil 12, and the areas between the sleeve 230 lead body 10 isbackfilled by means of medical adhesive or other polymeric material. Theelectrode coil 12 may be secured to the outer circumference of the leadbody 10 by means of a backfilling process as described in U.S. Pat. No.4,934,049, incorporated herein by reference in its entirety.

FIG. 7 illustrates the distal portion of the lead in the secondembodiment of the invention in which the stranded conductor 118 islocated internal to coil conductor 116. All illustrated elementscorrespond to identically numbered elements in FIG. 6, with theexception that a bore is provided in the proximal section 220A ofelectrode 16, and stranded conductor 118 is crimped therein.

While FIGS. 6 and 7 show the inter-connection of the stranded and coiledconductors at the tip electrode 16, these conductors may instead beconnected at a point proximal to the tip electrode, for example by useof a cross-bore crimp sleeve similar to sleeve 212, or by means of othertypes of welded, swaged or crimped connections as discussed above.

FIG. 8 is sectional view through the bipolar connector assembly 24 ofthe lead illustrated in FIG. 1, illustrating the first embodiment of theinvention. In this view, the proximal end of connector pin 36 is visiblein cross-section, and connector ring 32 is visible in cross-section.Connector pin 36 is coupled to coiled conductor 116 by means of aswaging core 200, which compresses conductor coil 116 and strandedconductor 118 between the interior lumen of connector pin 36 and theouter surface of swaging core 200, in a conventional fashion. Aninsulative sleeve 206 surrounds conductors 116 and 118, and extendsdistally, back through the connector assembly into molded sealing ringsleeve 28 (FIG. 1).

Surrounding connector pin 36 is a molded sealing ring sleeve 34, whichmay be fabricated of silicone rubber, which in turn is mounted to aspacer 204 which is typically fabricated of a harder plastic, such aspolyurethane. Spacer 204 is molded in situ between connector pin 36 andring electrode 32, and is maintained in mechanical interconnection withelectrode 32 by means of internal threading 208, as described in U.S.Pat. No. 4,572,605, issued to Hess, et al., incorporated herein byreference in its entirety.

FIG. 9 is a sectional view through the bipolar connector assembly 24 ofthe lead illustrated in FIG. 1, illustrating the second embodiment ofthe invention. All illustrated elements correspond to identicallynumbered elements in FIG. 8, with the exception that the strandedconductor 118 is located internal to coil conductor 116.

As in the case of FIGS. 6 and 7 above, other mechanisms may be employedto interconnect conductors 118 and 116 and connector pin 36, includingwelding, swaging, crimping and combinations thereof, as described above.Additionally, these conductors may instead be connected at a pointdistal to the connector pin, for example by use of a cross-bore crimpsleeve similar to sleeve 212, or by means of other types of welded,swaged or crimped connections as discussed above.

If it is not desired to mechanically interconnect on or both ends of thestranded conductor 118 to the coiled conductor 116, the internalstructure of the leads may correspond to those illustrated in FIGS. 6,7, 8 or 9 above, with the exception the stranded conductor 118 is simplynot crimped, swaged or otherwise coupled to the connector pin, electrodeor coiled conductor 118. In such embodiments, the stranded conductor mayextend the entire length of the coiled conductor or may extend over onlya portion of the length of the coiled conductor. While the FIGS. 6, 7, 8and 9 illustrate the coil and stranded conductor pair coupled to theconnector pin and tip electrode, it should also be understood that theinvention may also be usefully practiced in leads in which theseconductors are coupled to other connector elements, other electrodesand/or physiologic sensors located on the lead body. The interconnectionmethods of FIGS. 6, 7, 8 and 9 may also be used to connect the strandedconductor 118 to the coiled conductor 116 and to such other leadcomponents.

FIG. 10 illustrates a third embodiment of the invention. All numberedcomponents correspond to identically numbered components in the Figuresabove. In this embodiment, an uninsulated stranded conductor 118repeatedly enters and exits the internal lumen of the coiled conductor116, by passing between the coils. This embodiment, while more difficultto assemble, provides for in increase in the number of contact pointsbetween the stranded and coiled conductors, which may be beneficial inthe case of coil fractures as it will in many case shorten the distancewhich the stranded conductor must bridge as compared to the first andsecond embodiments and may provide for more consistent contacts betweenthe stranded and coiled conductors.

FIG. 11 illustrates a cross section through a fourth embodiment of theinvention All numbered components correspond to identically numberedcomponents in the Figures above. In this embodiment the strandedconductor 118 is located outside of coiled conductor 116 and isinsulated from conductor 116 over at least a portion of its length bymeans of an insulative tube 300, located exterior to conductor 116. Tube300 may be formed of PTFE or other insulative biocompatible plastic, andmay extend over all or some of the length of coiled conductor 116. Inthis embodiment, it is desirable that the ends of stranded conductor 118are mechanically coupled to the coiled conductor 116 on either side ofthe tube 300.

FIG. 12 illustrates a side, cut-away view through the fourth embodimentof the invention as illustrated in FIG. 11. All numbered componentscorrespond to identically numbered components in the Figures above

FIG. 13 illustrates a cross section through a fifth embodiment of theinvention All numbered components correspond to identically numberedcomponents in the Figures above. In this embodiment the strandedconductor 118 is located inside of coiled conductor 116 and is insulatedfrom conductor 116 over at least a portion of its length by means of aninsulative tube 302, located interior to conductor 116. Tube 302 may beformed of PTFE or other insulative biocompatible plastic, and may extendalong all or some of the length of coiled conductor 116. In thisembodiment, it is desirable that the ends of stranded conductor 118 aremechanically coupled to the coiled conductor 116 on either side of thetube 302.

FIG. 14 illustrates a side, cut-away view through the fifth embodimentof the invention as illustrated in FIG. 13. All numbered componentscorrespond to identically numbered components in the Figures above.

FIG. 15 illustrates an alternative mechanism for interconnecting astranded conductor 412 with a coiled conductor 416, both located withinan internal lumen of lead body 410. Conductive crimp sleeve 418 iscrimped to coiled conductor 416 by crimps 420. Optionally, a cylindricalcrimping core (not illustrated) may be inserted into the lumen of coiledconductor 416, prior to crimping. Stranded conductor 412 is coupled tothe crimp sleeve 418 by means of conductive sleeve 422, by the followingmethods. Stranded conductor 412 may be threaded through sleeve 422,which is then pushed onto crimping core 418, pulling stranded conductor412 along and compressing it between crimp sleeve 418 and sleeve 422. Inconjunction with this method, the interior of sleeve 422 may be providedwith threads or other internal texturing to frictionally engage strandedconductor 412. Alternatively, stranded conductor 412 may arrangedalongside crimp core 418 and sleeve 422, may then be pushed onto crimpcore 418, compressing conductor 412 between crimp sleeve 418 and sleeve422. In conjunction with this method, the exterior of crimp of sleeve418 may be provided with threads or other external texturing tofrictionally engage stranded conductor 412. As yet another alternative,sleeve 422 may simply be crimped around stranded conductor 412 andcrimping sleeve 418. Crimp sleeve 418 may take the form of a portion ofa connector pin or ring on the proximal end of the lead body or aportion of an electrode or other sensor on the distal portion of thelead body, or may simply be a cylindrical sleeve, employed to couple thestranded and coiled conductors at some point along the lead body.Plastic Sleeve 414 insulated stranded conductor 412 from coiledconductor 416 over a portion of their lengths.

FIG. 16 is a plan view of a defibrillation lead in which the presentinvention is practiced, employing a tip electrode taking the form of arotatable fixation helix 316. The lead of FIG. 16 is provided with anelongated insulative lead body 310, preferably fabricated of siliconerubber, polyurethane or other biocompatible elastomer. At the distal endof the lead, it carries an elongated defibrillation electrode 312, aring electrode 314 and a rotatable helical tip electrode 316, rotatablyand advancably mounted in insulative electrode head 318. Each electrodeis coupled to a conductor located within the lead body 310. Electrodes314 and 312 may correspond generally to conventionally available pacingand defibrillation electrodes. A cap member 319 is located at the distalend of electrode head 318 and serves to retain a monolithic controlledrelease device as discussed below.

The proximal end of the lead carries a connector assembly, beginningwith a molded lead bifurcation 320, which splits off two of theconductors within lead body 310 to a bipolar, in-line connector assembly324, generally corresponding to the IS-1 connector standard for pacingleads. However, other types of connector assemblies may also be adaptedto practice the present invention. Connector assembly 324 is providedwith a first set of sealing rings 328, a connector ring 332, a secondsealing rings 334 and connector pin 336. Connector pin 336 is rotatablymounted and is coupled to a rotatably mounted conductor which extendsthrough the lead body 310 to helical electrode 316. Connector ring 332is coupled to a conductor which extends through the lead body 310 toring electrode 314. A conductor coupled to defibrillation electrode 312extends into connector assembly 322, which carries a set of sealingrings 326 and is coupled to connector pin 330.

In the specific context of the lead illustrated in FIG. 16, theconductor coupling connector pin 336 to electrode 316 takes the form ofa monofilar or multifilar coiled conductor to allow passage of a stylettherethrough, while the conductors coupling ring electrode 314 toconnector ring 332 and coupling defibrillation electrode 312 toconnector pin 330 take the form of bundled, stranded wires, providedwith a coating of PTFE. However, the conductors coupling ring electrode314 and defibrillation electrode 312 may take the form of any of thevarious conductor types known for use in conjunction with implantableelectrical leads. If fewer electrodes are provided on the lead,correspondingly fewer conductors will be included. One or morephysiologic sensors may be added to the lead or substituted for one ormore of the illustrated electrodes. Also located within lead body 310 isa stranded wire conductor which extends along a length of the coiledconductor and which serves a mechanism for bridging a fracture of thecoiled conductor which occurs between the ends of the strandedconductor, as discussed above.

FIG. 17 illustrates a cross section through the lead illustrated in FIG.16. The lead body is provided with five lumens, including three circularlumens 350, 354 and 356 and two teardrop-shaped compression lumens 352and 358. Coiled conductor 360 is coupled to helical electrode 316 (FIG.16) and connector pin 336 (FIG. 16). On rotation of connector pin 336,conductor 360 transmits torque to rotate electrode 316, advancing it outthe distal end of electrode head 318 (FIG. 16) and screwing it intoheart tissue. Conductors 364 and 368 as illustrated are stranded orcabled conductors corresponding to conductors 112 and 114 (FIG. 2) andcouple connector pin 330 to defibrillation electrode 312 and connectorring 332 to electrode 314, respectively. Stranded conductor 362 iscoupled to coiled conductor 360 adjacent the proximal and distal ends ofthe lead, providing a redundant connector and tensile reinforcement inthe same fashion as conductor 118 (FIG. 2) discussed above. The wall oflead body 310 separating lumens 350 and 352 insulates conductor 362 fromconductor 360 between the points at which they are electrically coupled.Electrical interconnection of conductors 360 and 362 is by means ofrotating electrical couplings as described in conjunction with FIGS. 18and 19 below, which allow rotation of coil conductor 360 relative tostranded conductor 362.

FIG. 18 is a side cut-away view through the distal portion of electrodehead 318 of the lead of FIG. 16. Electrode head 318 is fabricated of arigid, biocompatible plastic such as a polyurethane, and is providedwith an internal longitudinal lumen 321. Cap 319 retains a toroidalmonolithic controlled release device 374, which serves to elute ananti-inflammatory steroid such as sodium dexamethasone phosphate, asdescribed in U.S. Pat. No. 4,972,848, issued to DiDomrnico andincorporated herein by reference in its entirety. Guide 363 engageshelical electrode 316 such that rotation of the electrode serves toadvance it out the distal end of electrode head 318 or withdraw it intolumen 321. Coiled conductor 360 is mechanically and electrically coupledto the proximal end of electrode 316 by conductive crimp sleeve 368,compressed by crimps 376. Crimp sleeve 368 is provided with acircumferential shoulder 378 which serves to limit distal movement ofhelix 316 by contact with radio-opaque marker ring 364 and which servesto limit proximal movement of helix 316 by contact with conductiveferrule 369.

Electrical interconnection of stranded conductor 362 and coiledconductor 360 is accomplished by ferrule 369 which is crimped tostranded conductor 362 by crimp 370 and is provided with contact means372 for coupling to conductive crimp sleeve 368. As illustrated thecontact means 372 is a conductive spring with individual turns offsetfrom one another to springingly contact both ferrule 369 and crimpsleeve 368 while allowing rotation and longitudinal movement of crimpsleeve 368, in a manner analogous to that illustrated in U.S. Pat. No.4,557,643, incorporated herein by reference in its entirety.Alternatively, coupling means in the form of other types of springcontacts, fine wire brushes or other known mechanisms for rotatableelectrical couplings may be substituted.

FIG. 19 shows a side, cut-away view through the lead of FIG. 16 in thevicinity of bifurcation 320. In this view, coiled conductor 360 andstranded conductors 362 and 364 are visible, exiting from lead body 310and entering into molded bifurcation 320. Interconnection of strandedconductor 362 and coiled conductor 360 is accomplished by ferrule 380coupled to conductor 362 by crimp 382, crimp sleeve 386 coupled tocoiled conductor 360 by crimps 388 and conductive spring 384. Thesecomponents function in the same way as their counterparts illustrated inFIG. 18 to couple the conductors while allowing rotational movement ofcoiled conductor 360. As in the case of FIG. 18, the known mechanismsfor making a rotating electrical connection may be substituted. Whilethe rotatable coiled conductor in this embodiment is coupled to ahelical electrode, it may alternatively be coupled to any otherelectrode which is deployed or manipulated by applied torque and mayalso be employed with any other mechanism requiring both applied torqueand an electrical connection.

While the embodiments described above are shown as alternatives itshould be understood that they also may be combined, with the locationand insulation of the stranded conductor relative to the coiledconductor varying along the length of the lead body. In addition, whilethe embodiments above all take the form of multiple lumen leadsfabricated using multi-lumen tubing, it should be understood that theinvention may also usefully be practiced in embodiments having only asingle lumen and in embodiments in which multiple lumens are provided bymeans of single lumen tubes located within larger diameter single lumentubes. As such, the disclosure above should be taken as exemplary,rather than limiting with regard to the scope of the claims whichfollow. In conjunction with the above disclosure, we claim:
 1. Animplantable medical lead comprising an elongated lead body having anelongated lumen therein;an elongated coiled conductor mounted within thelumen of the lead body; a stranded conductor, extending along the lengthof the lead body and coupled electrically to the coiled conductor at afirst location and a second location distal to and spaced from the firstlocation; wherein said coiled conductor is rotatably mounted in saidlumen.
 2. A lead according to claim 1 wherein said lead comprises meansfor coupling said stranded conductor to said coiled conductor while saidcoiled conductor rotates.
 3. A lead according to claim 1 or claim 2wherein said lead comprises a rotatably mounted electrical connectorlocated on a proximal portion of said lead body and coupled to saidcoiled conductor.
 4. A lead according to claim 3 wherein said leadcomprises a rotatably mounted electrode means located on a distalportion of said electrode body and coupled to said coiled conductor. 5.A lead according to claim 1 wherein said stranded conductor comprises aseven stranded conductor.
 6. A lead according to claim 5 wherein saidstranded conductor is made of MP35N alloy.
 7. A lead according to claim5 wherein said stranded conductor has an outer diameter of about 0.003inches.
 8. A lead according to claim 1 wherein said stranded conductoris located outside said lumen of said lead body.
 9. A lead according toclaim 8 wherein said lead body is provided with an additionallongitudinal lumen and wherein said stranded conductor is located withinsaid additional lumen.